Caterpillars have a rough time of it because nature keeps a balance. One of the many enemies of butterfly and moth caterpillars is this ectoparasitoid. It is a parasite that kills the host organism, thus is called a parasitoid. This parasitoid is different than most parasitiods we see in our caterpillars and chrysalids. This one feeds from the outside.

While walking Maggie and I found a black moth caterpillar with a lump on its head in the grass. Close examination revealed it to be a lump of larvae of this parasitoid. The vigerous active caterpillar was placed in a paper bag with food overnight. The next morning we opened the bag to move it to a rearing container indoors when we realized that the caterpillar was being sucked up by these little larvae of the parasitoid.

The next day the parasitoid larvae were pupae, hidden under the empty skin of the caterpillar.

Ectoparasitoid Euplectrus on a moth caterpillar

The caterpillar was so active it was difficult to keep it on my hand

It was placed in a brown bag overnight and the next morning ...

Peeling up one end of what was left of the caterpillar, ectoparasitoid larvae are seen feeding like little piglets

A closer view is not pretty

Winged adult critters emerged. After some research online, we were able to identify them as a type of parasitoid wasp. Further research indicates they are Euplectrus sp..

Later, while collecting a sample of every species of caterpillar we could find on oak trees in our area, we found these two caterpillars, clearly parasitized. The black caterpillar was as seen below. After peeling up the skin, the parasitoid pupae were revealed. The skin was simply that - just empty skin. No mush, no goo, just an empty flat skin like a deflated balloon.

Moth caterpillar with two ectoparasitoids attached.

This caterpillar was already an empty skin when we found it.

Peeling up the skin, parasitoid pupae are revealed lined up below.

Euplectrus wasp eggs are laid on a lepidoptera larva. Eggs are primarily laid on first to third instar Lepidoptera larvae. They feed from the outside. They inject venom which prevents the caterpillar from molting into the next instar. From egg to pupa takes about 13 days. According to sources, the host dies during the migration of the ectoparasitoid. After migrating the larvae consume the tissue of the host larva and nearly double in size before spinning their cocoons.